Sparking plug



March 14, 19539.

1.. GRAF- 2,150,500

SPARKING PLUG Filed April 1, 1957 jag. 5' Inventor: 0 Gzuf I P8P: 24:

Patented Mar. 14, 1939 UNITED STATES PATENT OFFICE SPARKING PLUG Application April 1, 1937, Serial No. 134,373 In Germany February 1'7, 1937 6 Claims.

This invention relates to ignition or sparking plugs.

.In the field of ignition or sparking plug construction it has hitherto been assumed that in the case of ignition plugs having a low ignition value the electrodes can project freely-into the combustion chamber, whilst the electrodes for ignition plugs of a higher ignition value must be placed as deeply as possible in the mass of the body of the plug. A series of constructions of ignition plugs of this character are known amongst which may be mentioned those in which a cup-shaped electrode is arranged opposite a casing-shaped mass electrode, preferably with the interposition of an intermediate electrode. In

these cases either the electrode system itself or in anycase the spark gap is screened relatively to the combustion chamber either by reason of the fact that the electrodes are retracted in the mass of the body of the plug or by reason of the fact that there is provided on the body of the plug a front structure, provided with apertures, which surrounds the spark gap.

Thorough investigations have shown that the previous views regarding the construction of ignition plugs with a high ignition value is unsatisfactory as regards the electrode arrangement and that at least in connection with particular forms of electrode it is not only possible but par- 0 ticularly advantageous to cause the spark gap to project from the body of the plug even in the case of ignition plugs of high ignition values. An ignition plug constructed in this way has the known advantage of effecting a good ignition and 35 thus of easy starting of the internal combustion engine, and at the same time the disadvantage of low ignition strength, which is otherwise associated with plugs of this type, is eliminated. An ignition plug constructed in this manner is in- 40 dependent of the ignition value in spite of predominating ignition properties.

In addition to the above mentioned arrangements of the spark gap the invention also resides in a series of steps which, partly known per se,

5 both in combination with the construction of the spark gap'and in multiple combination together and in part themselves produce substantial advantageous effects.

It is, therefore, an object of the present inven- 50 tion to provide an improved construction of sparking plug.

It is a further object of the invention to provide a sparking plug having a high ignition value in which the electrodes are so positioned as to cause 55 the spark gap to project from the body of the plug.

A further object is to provide a sparking plug including a central electrode and a mass electrode disposed within a groove in the lower face of the plug body, the electrodes being so positioned as to afford a spark gap located outside 5 the foot portion of the plug body in order to provide a construction of sparking plug with which easy starting of the engine may be efl'ected.

In order that the invention may be more clearly understood reference will now be made to the 10 accompanying drawing which shows by way of example preferred embodiments thereof.

In the drawing:

Figure 1 shows a vertical longitudinal section of an ignition plug according to the invention. 16

Figure 2 shows a similar section with a modified form of construction of the insulator foot.

Figure 3 shows an elevation. of an insulator, with a solid electrode, removed from the body of the plug. 20

Figure 4 shows a view of the plug.

Figure 5 shows a longitudinal section of the lower part of the plug body with a modified form of construction of one of the electrodes.

In the drawing like references designate the 25 same or similar parts.

The ignition plug consists of an insulator l with a central bore in which is mounted a rod 2 or ignition pin, hereinafter referred to as the ignition pin 2, which engages at its upper end in known manner, by means of a screw, with a part 3 on the upper screwed portion 3a on which there is located the cable securing nut 4. The insulator l is mounted in the plug body 6 by means of a nut 5, whilst a copper pressure ring I is fitted between the insulator and the nut 5. The plug body 6 is screwed by means of the screw thread 6a into the cylinder head.

The ignition pin 2 carries a shell or cup-shaped central electrode 8, whilst a rivet-like head 9, provided on the pin 2, presses the electrode 8 against the lower surface of the bottom part of the insulator, hereinafter referred to as the insulator foot. A gas tight joint between the lower end of the insulator foot and the upper surface 46 of the central electrode is obtained by applying pressure to the insulator l by tightening the part 3. Underneath the main part of the screw portion 3, which is preferably provided with cooling ribs, there is provided a cup-shaped cap H) which 50 surrounds the upper cylindrical part of the insulator body I. Between the surface of the insulator body I and the part of the cap l0 formed as an annulus there is preferably provided a resilient intermediate member II in the form of a spiral spring or in the form of a spring washer, whilst between the said spring washer or the like on the one hand and the upper part of the insulator I there may be provided a packing or spacing washer it. By means 0! the spring II, or means equivalent to a spring, the diflerences in the coeiiiclents of expansion of the insulator on the one hand and the pin 2 on the other hand are balanced so that the plug remains permanently gas tight. I

As the central electrode 8 during operation acquires a very high temperature and consequently expands correspondingly in a radial direction, and alter interruption oi! the ignition again contracts. provision must be made so that the i'or'ces acting in a radial direction in the central electrode are not transmitted to the lower part of the insulator foot as otherwise the insulator foot would burst. For this purpose the insulator foot and the upper surface of the central electrode. may be so constructed that the coeillcient of friction between these two surfaces is reduced to a considerable extent. In consequence of the necessary gas tightness and the tight pressing of the central electrode against the insulator foot necessitated thereby, this step will not always lead to the desired result, and it is, therefore, advisable to provide an intermediate layer 13 between the lower end oi! the insulator foot and the surface of the central electrode. This intermediate layer It must be so constructed that it is capable of following the expansion of the central electrode by its own change of shape on its under surface whilst the upper side of the intermediate layer It does not partake oi the movement of the under surface oi? the washer i3. The internal resistance to change of shape oi! this intermediate layer must thus remain below the force which is liable to be associated with the cracking of the insulator foot. It is therefore advisable to use for this purpose an asbestos packing washer.

Opposite the outer edge of the shell-like central I electrode 8 there is provided the mass electrode.

The mass electrode may, for example, be formed by a ring M, fitted into the foot 0! the plug body, of which the cross-section, for example, may be circular. This mass electrode may be pressed into a groove of the foot of the plug body. The mass electrode may also, as indicated in Figure 5, consist 01 an annular ring Ila 0! which the cross-section is triangular or trapezoidal, whilst this electrode ring may be fitted into a suitable groove of the foot of the plug body 6b.

The mass electrode may also be formed by a metal wire II, as shown in Figure 3, which is 01 conical shape and oi which the lower edge is opposite the upper edge of the shellor cup-shaped central electrode I. The mass electrode II has the same conical shape as the outside oi the insulator foot or the inside of the foot of the plug body. so that the mass electrode bears closely against the foot of the plug body on the one hand and the loot oi the insulator on the other hand.

InthetwocasesshowninFigures 1 spoil the lower end of the insulator toot is so constructed that within the gap between the two electrodes there is formed a space It in which the combustion gases are highly compressed and from which they escape with considerable energy on ignition in the form a! a circular cutting flame.

In the form of construction in Figure l the insulator is provided with a conical inner bore in which is greater than the diameter of the ignition pin 2 by such an amount that an outward spreading of the insulator body cannot take place as a result of heat expansion of the pin 2. In order to prevent distortion oi the ignition pin 2, that is to say a displacement oi the ignition pin 2 irom the axis of the bore la, the said ignition pin I is centered at two points, namely at its upper end in the part I, which in turn is centered relatively to the insulator by the cap II, and by means of a ring H provided on the ignition pin 2. This ring may be formed by a projection on the ignition pin 2 or by a ring fitted thereon. In the second case this ring may be formed of a material which is a poor heat conductor.

The bore la in the insulator body I serves to prevent the pin 2 from being heated by the plug body 6, 6a or the foot of the insulator l. The air located in the bore Ia constitutes an excellent heat insulator so that the rod 2 is considerably removed from the heating action oi! the insulator body. The removal of heat from the rod 1 is eilected through the part I and the nut l, whilst the part I may be provided with additional cooling ribs, as also the nut l. The insulator l itseli' may be provided with cooling ribs l8 formed thereon, whilst in the upper part of the plug body holes I! may be provided so as to permit of an air circulation.

As shown in Figure 2 there may be fitted between the lower part of the plug body and the lower part of the insulator foot a packing of poor heat conducting material, for example asbestos. In this manner the heat transmission from the lower part 0! the plug body to the insulator is prevented to a considerable extent so that the heat from the lower part of the plug body is conducted substantially into the cylinder head which is cooled by known means and, therefore. does not influence either the insulator or the ignition pin 2 so that the mass of the ignition pin 2 remains free for carrying away the electrode heat.

The insulator I may be provided in the interior thereof with 'a good heat conducting layer, which for example consists of a sprayed metal layer or a. tube provided thereon, so that the heat which enters the plug body at the lower end is conducted rapidly to the top and there can pass to the outside. The arrangement may be such that the inner heat radiating casing of the in sulator body or the tube is brought by a radially disposed extension into good heat conducting connection with the outer air. In order to prevent-the ignition pin 2 from being influenced by any heat radiated from an inner casing of this character the interior of the plug may be evacuated by pumping or the like as a vacuum or a rarefied air space is a particularly poor heat conductor.

The arrangements may also be such that the lower part of the cone of the insulator foot is protected by an asbestos layer or the like from the entrance of heat from the foot oi the plug -body, whilst from the point at which the temperature of the plug body is less than that of the insulator body it is possible to effect a heat flow from the upper part of the insulator foot to the plug body 6 by the insertion or a metal casing. In such a case the conical part of the insulator foot, for example within the range of the screw thread to or somewhat beyond this, is provided with a casing of poor heat conducting material whilst the part of the insulator foot above this is either surrounded by a suitably thick metal v casing or bears directly against the inner bore of the plug body. In this case the lower part of the insulator foot is preferably stepped so that at its lower end there is provided suillcient space for the introduction of the heat insulating intermediate layer 20. when constructing the mas electrode according to Figure 3 there may be inserted under the conical mass electrode IS a similar intermediate layer of poor heat conducting mate rial as shown with reference to Figure 2. Also inthiscaseitispossibletoinsulateonlythe lower part of the mass electrode against the insulator body by a poor heat conducting material, whilst the upper part of the mass electrode may be left uninsulated for the purpose of conducting the heat from the insulator body to the plug body.

What I claim is:

1. A sparking plug comprising a plug body, an insulator body mounted in said plug body, said insulator body having a tapered axial bore therein, arodlocatedinsaidboreandinspaced relation thereto, means for positioning said rod in said bore at opposite ends thereof, said insulator body projecting from the lower end of said plug body, a cup-shaped electrode secured to said rod and bearing against the end face of said insulator body, said cup-shaped electrode having a rim spaced from said insulator' body, and anearth electrode arranged in spaced relation to said central electrode, said plug body having an annular recess in the end face thereof, said earth electrode being located in said recess.

2.'A sparking plug comprising a plug body, an insulator body mounted in said plug body, said insulator body having a tapered axial bore therein,arodlocatedinsaid bore andinsp'aced relation thereto; means for positioning said rod insaid bore at opposite ends thereof, saidin sulator body projecting from the lower end of said plug body, a cup-shaped electrode secured to said rod and bearing against the end face of said insulator body, said cup-shaped electrode havinga rim spaced from said insulator body, and an earth electrode arranged in spaced relation to said central electrode, said earth electrode being in the form of a conical sleeve, said insulator body having a conical foot, whilst said plug body is provided with a conical bore, said conical sleeve being located between said conical foot and said conical bore.

3. A plug comprising a plug body, an insulator body molmted in said plug body. said insulator body having a tapered axial bore therein, a rod located in said bore and in spaced relation thereto, means for positioning said rod in said bore at opposite ends thereof, said insulator body projecting from the lower end of said plug body, a cup-shaped electrode secured to said rod and bearing ainst the end Qface of 3 said insulator body, said cup-shaped electrode having a rim spaced from said insulator body,

such as asbestos, located between said foot and said bore.

4. A sparking plug comprising a plug body, an insulator body mounted in said plug body, said insulator body having a tapered axial bore therein, a rod located in said bore and in spaced relation thereto, means for positioning said rod in said bore at opposite ends thereof, said insulator body projecting from the lower end of said plug body, a cup-shaped electrode secured to said rod and bearing against the end face of said insulator body, said cup-shaped electrode having a rim spaced from said insulator body, and an earth electrode arranged in spaced relation to said central electrode, the means for positioning said rim adjacent the central electrode being in the form of a ring of poor heat conducting material.

5. A sparking plug comprising a, plug body, an insulator body mounted in said plug body, said insulator body having a tapered axial bore therein, a rod located in said bore and in spaced relation thereto, means for positioning said rod in said bore at opposite ends thereof, said insulator body projecting from the lower end of said plug body, a cup-shaped electrode secured to said rod and bearing against the end face of said insulator body, said cup-shaped electrode having a rim spaced from said insulator body, and an earth electrode arranged in spaced relation to said central electrode, the hollow space remaining in the insulator body being evacuated.

6. A sparking plug comprising a plug body, an insulator body mounted in said plug body, said insulator body having a tapered axial bore therein, a rod located in said bore and in spaced relation thereto, means for positioning said rod in said bore at opposite ends thereof, said insulator body projecting from the lower end of said plug body, a cup-shaped electrode secured to said rod and bearing against the end face of said insulator body, said cup-shaped electrode having a rim spaced from said insulator body, and an earth electrode arranged in spaced relation to said central electrode, said plug body having an annular recess in the end face thereof, said earth electrode being in the form of an annular ring of trapezoidal cross-section and engaging said groove.

LEO GRAF 

